1. Field of the Invention
The present invention relates to an image display device adapted for use as display means in an electronic still camera, a video camera or the like, a semiconductor device adapted for use in various optical sensors, and optical equipment equipped with the image display device and/or the semiconductor device mentioned above, and more particularly to an image display device and/or a semiconductor device adapted for use in detection of line of sight or optical detection, optical equipment having such function of detection of line of sight or optical detection.
2. Related Background Art
The image display devices are available in different sizes, and are being used in various applications such as television, monitors for office equipment, monitors (view finders) of electronic still cameras or video cameras etc.
Also the image display devices are known in various types, such as a liquid crystal display device, CRT (cathode ray tube) a, plasma display, EL (electro-luminescence) display etc. Among these, the liquid crystal display device is being utilized in various applications because of various advantages such as light weight, possibility of compactization, ease of full-color display and low electric power consumption.
On the other hand, the apparatus for recording images on a silver halide-based film, namely the camera, has recently shown remarkable progress particularly in the automatic focusing technology. Within this field there is already known a technology for detecting the direction of the line of sight of the observer (photographer) and automatically focusing the phototaking lens to such observed position, as disclosed in the Japanese Patent Laid-open Application Nos. 1-241511 and 4-240438.
This invention aim at achieving, for example, convenient auto focusing function of larger freedom "by providing a finder device for observing an object, illumination means for illuminating the eye of the observer looking into the finder device, a condensing optical system for condensing the reflected light from the eye of the observer, photoelectric conversion means for receiving the condensed reflected light, and calculation means for calculating the direction of the line of sight of the observer from the output of the photoelectric conversion means, and controlling at least one of the phototaking condition setting means of the camera according to the result of calculation of the calculation means."
An example of the sight line detecting device will be schematically explained with reference to FIG. 1. An infrared light source 2901 constituting a point light source illuminates an eyeball 105 through a condensing lens 2902 and a half mirror 2903. The human eye can be considered as an adhered lens, with the front face 106a of the cornea, the rear face 106b thereof, the front face 108a of the lens and the rear face 108b thereof as the adhering faces or the interfaces, and the iris 107 is positioned close to the front face of the lens. The variations in the refractive index are different at these adhering faces, and the reflection occurs in the descending order of the front face of the cornea, the front face of the lens, the rear face thereof, and the rear face of of the cornea. Also the paraxial tracking indicates that the reflected images at the different interfaces, in response to a parallel incident light beam, are positioned as shown in FIG. 2, when the eyeball is seen from the front.
As shown in FIG. 2, the reflected images of the interfaces are focused at positions, measured from the front face 106a of the cornea, of 3.990, 4.017, 4.251 and 10.452 mm in the order of the 1st, 2nd, . . . faces. These values correspond to the standard shape and values, shown in the following, of the human eye.
standard radius of curvature of 106a=7.98 mm
standard radius of curvature of 106b=6.22 mm
standard radius of curvature of 108a=10.20 mm
standard radius of curvature of 108b=61.7 mm
refractive index between 106a-106b: n.sub.1 =1.376
refractive index between 106b-108a: n.sub.2 =1.336
refractive index between 108a-108b: n.sub.3 =1.406
refractive index to the right of 108b: n.sub.4 =1.336
These images are called Purkinje's images. The reflected images by the eye of the observer are guided by the inverse path, then reflected by the half mirror 2904, and enter a photoelectric converter 2905, on which the Purkinje's images reflected at different interfaces are focused. The Purkinje's images appear as point images arranged linearly on the optical axis of the eyeball but, if the line of sight is directed to either direction by the rotation of the eyeball, the illuminating light enters obliquely to the optical axis of the eyeball, so that the Purkinje's images move to positions deviated from the center of the pupil. Thus there can be observed plural Purkinje's images, because the amount and direction of movement of the Purkinje's image depend on the interface where the Purkinje's image is formed. The direction of the line of sight can be detected by electrically finding the movement of these Purkinje's images and, if necessary, the centers of the pupil and the iris.
This principle will be briefly explained with reference to FIGS. 3 and 4. Referring to FIG. 3, when the iris 3102, pupil 3103, Purkinje's 1st image 3104 and Purkinje's 2nd image 3105 are detected as illustrated on a device consisting of a two-dimensional array of photoelectric converting elements 3101, the elements for example of the 7th row and the 5th column provide the illustrated outputs. Thus a position (x.sub.5, y.sub.7) providing a 1st peak and a position (x.sub.10, y.sub.7) providing a 2nd peak are respectively detected as 1st and 2nd images, and the rotation angle of the eyeball can be calculated, according to FIG. 4, from the amount of positional aberration of the two images, or the amount of displacement of the Purkinje's images.
FIG. 1 shows a conventional configuration of a sight line detecting device for auto focusing control by the feedback of thus detected information of the watching point of the observer.
As shown in FIG. 1, the sight line detecting device includes a light-emitting device used for the light source 2901 and a photosensor used for the photoelectric converter 2905. Also apart from the detection of the line of sight, there are already known various light-emitting devices and photosensors, usable for the purpose of projecting light to an object and detecting the reflected light thereby detecting the image or position of the object.
In a signal processing system for reading the coordinates of an optical image by light irradiation, as shown in FIG. 5, the light source 3301 need not be an array but can be a point light source as long as it can uniformly illuminate the entire object 3302 which randomly reflects the light at the surface. For this reason there is generally used an inexpensive light-emitting element such as an LED. By uniform illumination on the object 3302, the light containing positional information enters a photosensor 3304 through an optical system 3303 of the system.
The photosensor 3304 requires at least one-dimensional array unless it is not equipped with a geometrical scanning mechanism. The photosensor 3304 is generally composed of a photodiode array or the like for simple positional detection, and a CCD for more complex image recognition.
Attention is now being attracted to a recently discovered light-emitting phenomenon in Si which is an indirect transition semiconductor material. For example, monocrystalline silicon emits light at discontinuity of the crystal, such as a defect, when a large current of the order of 1 mA is given. Also at the interface of polysilicon and monocrystalline silicon, the light emission is possible by the current force. A similar light-emitting phenomenon is also known in amorphous silicon. The most famous light-emitting phenomenon is reported by Axel Richter et al. in "Current-Induced Light Emission from a Porous Silicon Device", IEEE Electron Device Letters, Vol. 12, No. 12, December 1991, pp. 691-692.
The porous silicon emits red light with a good efficiency, and is attracting attention as the future light source.
However, for applying the aforementioned detection of the line of sight of the observer to an image display device such as a view finder, there are required a new light source for such sight line detection, an optical system for condensing the light in a predetermined position in the view finder. Stated differently, independently from the light coming for example from the light, there is required light of a desired intensity, preferably invisible to the human eyes.
Consequently there is required a space for the light source for the sight line detection, the photoelectric converting device, and the optical system if necessary, leading often to the drawbacks of increased size and cost of the equipment.
More specifically there are required anew an LED light source 2901 for obtaining infrared or near-infrared light for the detection of the line of sight, and a light-splitting half mirror 2904, and these components not only increase the dimension of the equipment in optical designing but also the number of component parts, thus raising the cost.
Besides, if the light emission intensity of the LED light source is increased in order to improve the sensitivity of detection, increases will result in the power consumption and in heat generation, hindering the compactization and power saving of the equipment. Furthermore, there is requirement for avoiding entry of an unnecessary amount of light into the eyeball.
As explained above, when the photoelectric conversion means and the driving means therefor, for the detection of the line of sight, are provided independently from the main image display device, there are required additional space and components for such detecting function, leading to an increased cost of the product.
On the other hand, in an optical signal processing system as shown in FIG. 5, the light source and the photosensor are generally constructed independently, and the light source 3301 is usually composed of a semiconductor device capable of providing a high intensity such as a Ga--As device, or a small lamp such as an incandescent or fluorescent lamp. It will be easily understood that the integration of such light source and the aforementioned photosensor 3304 on a same chip is extremely difficult.
Also there is required an additional optical system for guiding the light from the above-mentioned light source 3301 to the object 3302, and this increases the volume of the entire system.
Also the system including the optical system 3303, generally involving the imaging process, requires a dimension several times as large as the focal length of the lens contained in the optical system 3303. Such increase in the dimension of the system is never desirable, though the extent of such increase is dependent on the system.
Also in terms of the cost, the III-V semiconductor device, such as Ga--As device, is more expensive in comparison with the Si-based semiconductor device. Besides the cost increase of the system, the presence of a non-essential additional optical system should be avoided.